Control of shunt field generators



Nov. 8, 1949 R. o. PERRINE 2,487,172

CONTROL OF SHUNT FIELD GENERATORS Filed Sept. 9, 1948 ,L @MWM MM; 6. @mm

Patented Nov. 8, 1949 CONTROL OF SHUNT FIELD GENERATORS Robert 0. Perrine, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application September 9, 1948, Serial No. 48,473

2 Claims.

This invention relates to the control of shunt field generators and more particularly to control of a plurality of such generators when operated individually or in parallel to supply power to a common load.

In certain types of service it is desirable that a plurality of shunt field generators driven by the same or individual prime movers be arranged to operate individually or in parallel to supply a load under the control of more or less conventional types of voltage regulators. When operated in parallel to supply the load, control of the generators by their individual voltage regulators has not been too satisfactory. Due to differences in the actual voltage settings between the associated voltage regulators of the respective generators, considerable unbalance in the division of the load current between the generators occurs. While special types of voltage regulators have been devised to improve the balance in the division of the load, their use has generally complicated the control systems and required the use of additional switching apparatus. A system affording improved balance with respect to division of the load current between parallel operated generators and permitting the use of conventional single operating coil voltage regulators in conjunction therewith has long been desired.

It is an object of the present invention to provide a control system of such character.

Another object is to provide a control system of the aforementioned type without impairing the operation of any generator, under the control of its associated voltage regulator, alone to supply the load, and

Another object is to provide a control system of the aforementioned type which requires only conventional switching apparatus to effect changes from single to plural generator supply of the load.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates a preferred embodiment of the invention which will now be described, it being understood that the embodiment illustrated is susceptible of modification in respect of its details without departing from the scope of the appended claims.

The single figure of the drawing is a diagrammatic showing of a power supply system together with a pair of shunt field generators and a control system for said generators.

Referring to the drawing, it shows a power supply system comprising a pair of generators l0 and H for supplying direct current power to bus bars l2 and I3 which in turn supply power to a battery 14 and a load 15 as shown. Generally considered the system is such that with either one of the generators operating alone or with both generators operating together in parallel direct current power will be supplied to bus bars I 2 and I3 at the required voltage. The system shown is intended primarily for use on Diesel-electric or turbo-electric locomotives for supplying power to electrically operated auxiliaries thereon, although it is to be understood that the system may be used for other purposes.

It is assumed that generators l0 and l I are substantially identical in construction and have equal ratings. Although not shown, it may be assumed that the generators are driven by the same prime mover or by prime movers which are individual to the generators.

As shown the generators are of the shunt field type and are provided respectively with shunt field windings l0 and H. The generators have their negative terminals connected to the bus bars l2 in series with resistors Ill and li respectively. Resistors Ill and ll should be of equal value and may take the form of separate resistances as shown, or the resistances may be inherent in each of the generator connections.

The generators are provided with voltage regulators l6 and I1 respectively for regulating their output voltage over their operating ranges. These regulators are shown as carbon pile regulators, but it is to be understood that any other suitable type may be used. It is assumed that the regulators shown are each of one of the conventional types of carbon pile Voltage regulators, identical in construction, and, in so far as possible, substantially the same with respect to their actual voltage settings.

The regulators are provided with carbon pile resistance elements H5 and I! respectively which are connected in series circuit relation with the shunt field windings of their associated generators. The regulators are also provided with operating coils Ili and I! which are of equal internal resistance and which are connected at corresponding ends to the negative terminals of their associated generators. The other end of coil "5 is connected to a point intermediate 2. pair of resistors I8 and 19 which are connected in a series circuit relation between the positive terminal of generator l0 and the negative terminal of generator ll. Similarly, the other end of coil I! is connected to a point intermediate a pair of resistors 20 and 2| which are connected in series circuit relation between the positive terminal of generator II and the negative terminal of generator [0. It is assumed that resistors l8 and 20 will be equal in value and similarly that resistors l9 and 2| will be equal in value.

As will be noted the aforedescribed connections for the operating coils l and il of regulators l6 and I! diff'r frofii the conventional c'on-nec= tion of the same which would be directly across the negative and positive terminals of their as: 1

sociated generators. In the present embodiment the coils are connected at one i-id to" the negative terminals of their associated generators at the other end to the intermediate points oi voltagedividers which are connected between the positive terminal of their associatedgenerators and the negative terminal of the other gener tor; one such voltage divider comprising the resistors I8 and I9 and the otheiqvoltage divider comprising the resistors 20 and, 2 i. As will be later more fully explained this arrangement airqrus irriproved balance in division or the load current between th geiieratais both are operating and connected ts supply power to Bus bai s l2 and I3.

As is fionvefitioiial, each of the generators is provided with a knife switch and a reverse eurrent relay for controlling the connection of the generates stress bus bars i2 ans l3. Thus genei ator ID has associated therewith a knife switch 22 and a reverse current relay 23 and similarly the generator I I has associated therewith a knife 2 1 and a reverse current relay 25. N The advantages "of the preferred control system cbinparing th results that can be obtained thereby with the conventional arrangement of the voltage regulators under assumes sets of conmeans which might be encountered practice. As a first ease assume that ins ea of the a i-- range'inge'nt seq we and described herein, that the coils 16 and 11 respectively of regulator's l6 and H are each directly connected across the pen;- tive and negative terminals of their associated generators in the bnventipnai Then the following equations will hold true for any given set of operating cohditiohswhen generators ill and H are operated in parallel to suppl the load:

where *E; is the terminal voltage of generator 1-0 E2 is the terminal voltage of generator *H :Vi is the actual voltage setting of regulator H3 V2 is the actual voltage setting of regulator H 111's thecun-entsup'pirea tvgefieiat'or in its is the current supplied by generator M 1 1s t'ile'fiotai seemed which teens nan R sjthefrsistance (if each or the resistors 1t an Tl rs ieeeveiy By "way of a spec i ficjei'iainple, assume that the desired b'us voltageis 75 volts, that although tl ie tire rated voltage sett ngs 'or the regiiiatdrs rs 7'5 volts the actual fveita 'e setting "of regmators q a n '|1 ar e15.5vo1tsane 74:5 volts respectively,

that the total load current "is 150 amps. "and that h'reinb'efore described best be s own by the resistors l and l I are each .02 ohm. Then substituting these values in Equations 1, 2 and 3:

E E 75.5-74.5 1 volt b 75.5;74.5 E=75-1 5=73.5 volts and since Il+I2= Ii IOO amp I2=50 amps.

a 1 voltdifference in the voltage setting er reguiaters i9 and I? will cause a difference of amps. between the current supplied by the generator [9 and that supplied by generator H.

New considering the preferred control system hereinbefore described, the following equations can be derived by Ohms and Kirchhofis laws and will hold true for any given set of operating conditions when generators Ill and H are operated in parallel; provided, that theinternal resistance of the operating coils I6 and [l are equal; that resistance 8 and 2B are of equal ohmic value and that resistors l9 and 2! are of equal ohmic value:

where E1, E2; VnVz, Vu, I, and R are the same as previously indicated for Equations 1, 2 and 3.,

and where:

n is the ohmc value of each or the resistors Ia and 20 v 5% the ohmic Vallle 0f the internal resistance bf coils 1t and 'l 1 f3 is the ohmic value of each of the resistors 19 and 2i Qn e highly satisfactory system is afiorded by making the resistors l8, i5, 21? and '2'] one-half the ohmic value of the internal resistance of the coils [6 and I l and thus Equations 4, 5 and 6 may be reduced to the following forms:

It will be apparent from Equation 8 -that in order to maintain a bus voltage of volts that 'the rated voltage settings of regulators +6 and 1:1 will have to be 3016 volts (assuming -IR 2 =1.5 volts) instead "of 75 volts.

Byway of a specific example assume that with the preferred 'system of c'on'trol (with the resistars 18, 19, 20 and "21 er equal ohmic value and equal to one-half the internalresistance of coils 1*69 and 1 that it is desired to maintain :a bus vaults-g2; of 75 "volts, that the rate'd vol-tage -settings (if regii la'tors "IF-arid 1 15 3016 volts, that theme-- tual voltage settings "of regulators H5 and H are 3225 volts and 31.75 volts respectively. Further assume that the load current to bes'upplied by iafait0f$ "F0 and ll is- 150*amp. and that there- EFEZ: 1.2

=.417 volt V =1.25(32.25l31.75) =78.5 volts and since I1+Iz=150 amps.

The preferred control system thus affords a considerable improvement over the conventional system with respect to the division of the total load current between the two generators. Although the difference in the assumed actual voltage setting of the regulators was 1 volt in the example demonstrated in connection with the conventional system and only .5 volt in the example demonstrated in connection with the preferred system, the two differences are about the same when considered in percentages of the rated regulator voltage settings. Therefore a comparison of the results is believed to be in order. Even if the assumed actual voltage settings of the regulators used in the example Worked out in connec tion with the preferred system were chosen to have a difference of 1 volt, there would still be an improvement in the division of the load current between the two generators.

The control system in no way impairs the op Where Vb, I, R, r1, m, and T3 are as previously indicated, and where:

V is the actual voltage setting of the voltage regulator If n is equal 13013 and each of the same is equal to one-half the ohmic value of m, then Equation 10 may be reduced to the following form:

By way of example, assume that generator II is idle and disconnected from bus bars I2 and I3. Also assume that resistors l8 and ii! are of equal ohmic value and equal to one-half the internal resistance of coil l6". Further assume that the actual voltage setting of regulator I6 is 32.25 volts, that the load current is 150 amps. and that the resistor lll is .02 ohm. Substituting in Equation 11:

Vb=(2.5 32.25) (2 150 .02 Vb=80.63-6=74.63 volts Thus generator I 0 operating alone is capable of supplying the rated load at substantially the desired bus voltage. Similarly it can be shown that generator H operating alone will function in a like manner.

While in connection with the preferred control system hereinbefore described the generators involved were assumed to be of qual ratings, this system may be also used in connection with generators of unequal ratings with the same beneficial results if the resistors l W and ll are made proportional in ohmic value to the ratings of their respective associated generators.

What I claim as new and desire to secure by Letters Patent is:

l. The combination with first and second generators having shunt field windings, first andsecond buses with the first of which the armatures of said generators have for like terminals individual connections including resistance proportional to the respective generator ratings and means for connecting other like terminals of said generators in parallel or singly to said second bus, of interconnections between armature terminals of each generator and the opposite armature terminals of the other generator, voltage dividers individualized to said interconnections, and separate shunt field regulators for said generators, said regulators having individual control windings connected between the first mentioned armature terminals of their respective generators and taps of the voltage dividers connected to the second mentioned armature terminals of their respective generators.

2. The combination with equally rated first and second generators having shunt field windings, first and second buses with the first of which the armatures of said generators have for like terminals individual connections including equal values of resistance and means for connecting other like terminals of the armatures of said generators in parallel or singly to said second bus, of interconnections between armature terminals of each generator and the opposite armature terminals of the other generator, like voltage dividers individualized to said interconnections, and separate shunt field regulators for said generators, said regulators having individual control windings connected between the first mentioned armature terminals of their respective generators and like taps of the voltage dividers connected to the second mentioned armature terminals of their respective generators.

ROBERT O. PERRINE.

No references cited. 

